Scientists have launched the world's biggest investigation into the effects of mobile phones on the developing brains of children.

The Study of Cognition, Adolescents and Mobile Phones (Scamp) will focus on mental functions such as memory and attention which continue to develop into the teenage years.

The World Health Organisation (WHO) has ranked forward-looking studies of the effects of mobile phones on children and adolescents as a "highest priority research need".

Current health guidelines say that children under 16 should be encouraged only to use mobile phones for essential calls, and where possible to use a hands-free kit or to send text messages. When they do have to make calls, they are advised to keep them short.

About 2,500 school children will be tested at age 11 and 12 and undergo a further assessment two years later. Most children start to own a mobile phone at around 11 or 12.

More than 160 secondary schools in the outer London area have received invitations to enrol pupils into the study.

Professor Patrick Haggard, deputy director of the Institute of Cognitive Neuroscience at University College London and chairman of the Scamp steering committee, said: "This study has two particularly valuable aspects: it attempts to estimate the children's exposure to radio frequency fields as precisely as possible, and it uses a carefully-designed suite of tests to measure many of the key cognitive functions that are developing during adolescence."

An estimated 70pc of 11 to 12 year olds now own a mobile phone, rising to 90pc by age 14.